(1) Field of the Invention
The present invention relates to a manufacturing method of a nitride semiconductor device and to a nitride semiconductor device.
(2) Related Art
Recently, many efforts are put into development relating to nitride semiconductor devices which are usable as a light source of next-generation optical disks of large capacity. One example is shown in International publication No. WO 03/038957A1.
A nitride semiconductor device is manufactured by subjecting each of nitride semiconductor layers to crystal growth on a nitride semiconductor substrate, using a MOCVD (metal organic chemical vapor deposition) method.
FIG. 1 is a perspective diagram schematically showing one example of such a nitride semiconductor substrate.
A nitride semiconductor substrate 1701 is made of: dislocation concentrated regions 1704, 1705, 1706, and 1707 which have concentrated therein defect crystals and align as stripes that pass through the nitride semiconductor substrate 1701 from a front surface 1702 to a back surface 1703; and low dislocation regions 1708, 1709, and 1710 which are normally crystallized regions. The width of each of the low dislocation regions 1708, 1709, and 1710 (i.e. the distance between each adjacent dislocation concentrated regions) is about 400 μm, for example.
On the front surface 1702 of the nitride semiconductor substrate 1701, semiconductor crystal growth is conducted using the MOCVD method for example, thereby obtaining a nitride-semiconductor layer structure.
FIG. 2 is a schematic diagram showing a layer structure of a conventional nitride semiconductor generated as in the above way, which is cut in a direction orthogonal to a direction in which the dislocation concentrated regions extend. On the front surface 1702 of the nitride semiconductor substrate 1701, crystal growth layers 1801, 1802, and 1803 are formed. The film thickness of the crystal growth layers 1801, 1802, and 1803 is not constant. In other words, the crystal growth layers 1801, 1802, and 1803 are thick in end portions 1804 and 1805, which are in the vicinity of the dislocation concentrated regions 1704 and 1705 respectively, compared to a center portion 1806.
So as to produce a nitride semiconductor laser device from a nitride semiconductor having such crystal growth layers 1801, 1802, and 1803, provision of waveguides in stripe formation becomes necessary so as to obtain a light trapping structure. There are various methods for forming such waveguides. Among such methods, ridge-type waveguides are formed using an etching technology by which depth and width are precisely controlled to an accuracy of about 1/100 μm.
However, if crystal growth layers have inconsistent film thickness, etching in the waveguide forming process will be uneven, and so a resulting nitride semiconductor laser device will have problems such as characteristic deterioration and yield reduction.